Transmission belt

ABSTRACT

A power transmission belt includes a belt body made of an elastomer, and a cord made of carbon fibers and provided to be embedded in the belt body and to form a helical pattern having a pitch in the belt width direction. When the cord is viewed from a side orthogonal to its length direction, an angle θ of an outermost filament in the filament bundle of the carbon fibers forming the cord with respect to the length direction of the cord is 8° or more to 20° or less.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No.PCT/JP2021/024895 filed on Jul. 1, 2021, which claims priority toJapanese Patent Application No. 2020-115525 filed on Jul. 3, 2020. Theentire disclosures of these applications are incorporated by referenceherein.

BACKGROUND

The present invention relates to a power transmission belt.

A power transmission belt using a cord made of carbon fibers has beenknown. For example, Japanese Unexamined Patent Publication No.2005-24075 discloses a toothed belt in which a cord made of carbonfibers is embedded in a belt body made of rubber.

SUMMARY

The present invention is directed to a power transmission belt includinga belt body made of an elastomer, and a cord made of carbon fibers andprovided to be embedded in the belt body and to form a helical patternhaving a pitch in a belt width direction. When the cord is viewed from aside orthogonal to its length direction, an angle of an outermostfilament in a filament bundle of the carbon fibers forming the cord withrespect to the length direction of the cord is 8° or more to 20° orless.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a piece of a toothed belt of anembodiment.

FIG. 1B is a longitudinal cross-sectional view of a portion of thetoothed belt of the embodiment.

FIG. 2 is a front view of a cord embedded in a toothed belt body, asviewed from a side orthogonal to the length direction.

FIG. 3A is a first diagram illustrating a method for forming the toothedbelt according to the embodiment.

FIG. 3B is a second diagram illustrating the method for forming thetoothed belt according to the embodiment.

FIG. 3C is a third diagram illustrating the method for forming thetoothed belt according to the embodiment.

FIG. 4 is a view of a layout of pulleys of a belt running tester.

DESCRIPTION OF EMBODIMENT

An embodiment will be described in detail below with reference to thedrawings.

FIGS. 1A and 1B illustrate a toothed belt B of an embodiment. Thetoothed belt B of the embodiment is an engagement power transmissionbelt and is advantageously used for high load transmission of machinetools, printing machines, textile machines, and injection machines, forexample. The toothed belt B of the embodiment has a belt length of, forexample, 500 mm or more to 3000 mm or less. The toothed belt B of theembodiment has a belt width of, for example, 10 mm or more to 200 mm orless. The toothed belt B of the embodiment has a (maximum) beltthickness of, for example, 3 mm or more to 20 mm or less.

The toothed belt B of the embodiment includes an elastomer-made endlesstoothed belt body 11 made of polyurethane resin. The toothed belt body11 includes a flat band portion 111 having a horizontally elongatedrectangular cross-section and a plurality of teeth 112 provided on theinner periphery of the flat band portion 111 so as to be integraltherewith. The teeth 112 are provided at a constant pitch in a beltlength direction.

Examples of the tooth profile of the each tooth 112 in the side viewinclude an arc tooth profile of the super torque synchronous (STS) beltsin which both sides of the tooth are bowed outward in the form of an arcand a trapezoidal tooth profile. The number of teeth 112 is, forexample, 30 or more to 400 or less. The teeth 112 each have a width (themaximum dimension in the belt length direction) of, for example, 2 mm ormore to 10 mm or less. The teeth 112 each have a height of, for example,2 mm or more to 8 mm or less. The teeth 112 are arranged at a pitch of,for example 8 mm or more to 14 mm or less.

The polyurethane resin forming the toothed belt body 11 is obtained byheating, pressurizing, and curing an urethan composition which isobtained by blending a curing agent, a plasticizer, and the like to aurethan prepolymer.

The urethan prepolymer is a relatively low molecular weight urethancompound which is obtained by a reaction between an isocyanate componentand a polyol component and having a plurality of NCO groups at itsterminals. Examples of the isocyanate component include tolylenediisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Examples ofthe polyol component include poly tetramethylene ether glycol (PTMG).The urethan prepolymer may be composed of a single urethan prepolymer ora plurality of urethan compounds blended.

Examples of the curing agent include amine compounds such as1,4-phenylene diamine, 2,6-diamino toluene, 1,5-naphthalene diamine,4,4′-diamino diphenylmethane, and 3,3′-dichloro-4,4′-diaminodiphenylmethane (MOCA). The curing agent suitably contains one kind ortwo or more kinds of them. The amine compound serving as a curing agentis suitably blended to have an a value (NH₂ group/NCO group) of 0.70 ormore to 1.10 or less. The a value is a ratio of the amount of NH₂ groupsby mole in the curing agent to the amount of NCO groups by mole in theurethan prepolymer.

Examples of the plasticizer include: dialkyl phthalates such asdibutylphthalate (DBP) and dioctyl phthalate (DOP); dialkyl adipatessuch as dioctyl adipate (DOA); and dialkyl sebacate such as dioctylsebacate (DOS). The plasticizer suitably contains one kind or two ormore kinds of them. The plasticizer is blended at 3 parts by mass ormore to 20 parts by mass or less relative to 100 parts by mass of theurethan prepolymer.

Example of the other compound ingredients include a colorant, anantifoaming agent, and a stabilizer.

The polyurethane resin forming the toothed belt body 11 has a hardnessof, for example, 70° or more to 100° or less. The hardness of thepolyurethane resin is measured in accordance with JIS K 7312: 1996.

The toothed belt B of the embodiment includes, as illustrated in FIG. 2, a cord 12 made of carbon fibers and embedded in the flat band portion111 of the toothed belt body 11. The cord 12 has a diameter D ofsuitably 0.4 mm or more to 2.7 mm or less, more suitably 0.5 mm or moreto 2.4 mm or less, in terms of obtaining excellent durability.

The carbon fibers forming the cord 12 are suitably PAN-based carbonfibers, in terms of obtaining excellent durability. Filaments F of thecarbon fibers each have a diameter of suitably 4 μm or more to 9 μm orless, more suitably 6 μm or more to 8 μm or less.

The total number of filaments F of the carbon fibers forming the cord 12is suitably 3000 (3K) or more to 60000 (60K) or less, more suitably 9000(9K) or more to 54000 (54K) or less, yet more suitably 12000 (12K) ormore to 48000 (48K) or less, in terms of obtaining excellent durability.The carbon fibers forming the cord 12 have a fiber fineness of suitably200 tex or more to 4000 tex or less, more suitably 600 tex or more to3600 tex or less, yet more suitably 800 tex or more to 3200 tex or less,in terms of the same.

The cord 12 is suitably a twisted yarn, in terms of obtaining excellentdurability. The twisted yarn forming the cord 12 includes a single twistyarn, a plied yarn, and a lang's lay. The cord 12 of the twisted yarn issuitably a single twist yarn obtained by twisting a filament bundle ofthe carbon fibers in one direction. For the cord 12 of the single twistyarn, either an S-twist yarn or a Z-twist yarn may be used, or both ofthem may be used.

If the total number of filaments F of the carbon fibers forming the cord12 of the single twist yarn is less than 24000 (24K), the number oftwists of the cord 12 per 10 cm length is suitably 2.0/10 cm or more to25.0/10 cm or less, more suitably 3.0/10 cm or more to 19.0/10 cm orless, yet more suitably 5.0/10 cm or more to 11.0/10 cm or less, interms of obtaining excellent durability. If the total number offilaments F of the carbon fibers forming the cord 12 of the single twistyarn is 24000 (24K) or more, the number of twists of the cord 12 per 10cm length is suitably 1.5/10 cm or more to 7.5/10 cm or less, moresuitably 2.3/10 cm or more to 6.6/10 cm or less, yet more suitably3.5/10 cm or more to 5.5/10 cm or less, in terms of obtaining excellentdurability.

When the cord 12 is viewed from a side orthogonal to its lengthdirection, an angle θ of an outermost filament F in the filament bundleof the carbon fibers forming the cord 12 with respect to the lengthdirection of the cord 12 is 8° or more to 20° or less. The angle θ ofthe filament F with respect to the length direction of the cord 12 issuitably 8° or more to 20° or less, more suitably 10° or more to 19° orless, in terms of obtaining excellent durability.

The cord 12 is provided to form a helical pattern with a pitch in thebelt width direction. The cord 12 may be made of two yarns of theS-twist yarn and the Z-twist yarn arranged in a double helix form. Thecords 12 are disposed to extend in parallel with each other at intervalsin the belt width direction, and the number of cords 12 per 10 mm beltwidth is suitably 3/10 mm or more to 16/10 mm or less, more suitably4/10 mm or more to 15/10 mm or less, in terms of obtaining excellentdurability. The cord 12 is provided to form a helical pattern with apitch in the belt length direction. Thus, its length direction isinclined with respect to the belt length direction. However, the angleof the inclination is very small. Thus, the angle θ of the outermostfilament of the filament bundle of the carbon fibers forming the cord 12with respect to the length direction of the cord 12 is substantially thesame as the angle of the filament F with respect to the belt lengthdirection.

The cord 12 has been suitably subjected to adhesion treatment such asimmersing it in a liquid adhesive agent and then drying before molding.

The toothed belt B of the embodiment further includes unwoven fabric 13embedded along the belt length direction on the inner peripheral side ofthe toothed belt body 11 from the position at which the cord 12 isembedded in the belt thickness direction. The unwoven fabric 13 may bemade of a single sheet or a plurality of sheets.

The unwoven fabric 13 contains polyurethane resin forming the toothedbelt body 11, and provided to form a layer in a side view. Portions ofthe unwoven fabric 13 corresponding to the respective teeth 112 extendinside the teeth 112 so as to bulge toward inner periphery in a sideview and expand thickly in the belt thickness direction. Portions of theunwoven fabric 13 corresponding to the portions between the teeth 112are in contact with the cords 12 and are compressed in the beltthickness direction to be thin.

Examples of a fiber material forming the nonwoven fabric 13 includenylon fibers, polyester fibers, aramid fibers, polyketone fibers, andcarbon fibers. The unwoven fabric 13 may be made of a single kind offibers, or a mixture of a plurality of kinds of fibers.

The unwoven fabric 13 has been suitably subjected to adhesion treatmentsuch as immersing it in a liquid adhesive agent and then drying beforemolding.

The belt tension T_(0.1) per 1 mm belt width at 0.1% of a belt extensionrate of the toothed belt B of the embodiment is suitably 30 N/mm ormore, more suitably 45 N/mm or more in terms of obtaining excellentdurability, and is suitably 50 N/mm or less, more suitably 45 N/mm orless in terms of avoiding impairing of flex fatigue resistance.

The belt tension T_(0.1) is determined as follows. In a 25° C.atmosphere, the toothed belt B according to the embodiment is wrappedaround a pair of flat pulleys with a pulley diameter of 95.4 mm in abelt tensile tester such that a belt backface comes into contact withthe flat pulleys. Then, one of the flat pulleys is separated from theother flat pulley at a speed of 50 mm/min. At this time, therelationship between displacement between the flat pulleys in pair andthe tension detected, starting at the time of generation of the tensiondetected via either one of the flat pulleys in pair, is recorded. Then,the displacement between the flat pulleys in pair is doubled tocalculate the amount of extension of the belt, which is then divided bythe belt length of the toothed belt B according to the embodiment undera no-load condition. Thus, the displacement between flat pulleys in pairis converted into the belt extension rate. Further, the tension detectedis divided by 2 to calculate the belt tension, which is then divided bythe belt width of the toothed belt B according to the embodiment. Thus,the tension detected is converted into the belt tension per 1 mm beltwidth. Then, the belt tension T_(0.1) is determined based on therelationship between the belt extension rate and the belt tension.

In the toothed belt B according to the embodiment with such aconfiguration, when the cord 12 is viewed from a side orthogonal to itslength direction, an angle θ of an outermost filament F in the filamentbundle of the carbon fibers forming the cord 12 with respect to thelength direction of the cord 12 is 8° or more to 20° or less.Accordingly, excellent durability can be obtained. This is presumablybecause the filaments F of the carbon fibers which are a brittlematerial forming the cord 12 is prevented from being excessivelydistorted.

Now, a method for forming the toothed belt B of the embodiment will bedescribed.

First, as shown in FIG. 3A, a cylindrical inner mold 31 is covered withthe unwoven fabric 13, and the cord 12 is then spirally wound around it.At this time, on the outer periphery of the inner mold 31, recesses 32with cross sectional shapes corresponding to the respective teeth 112extending axially are provided at a constant pitch at intervals in acircumferential direction, and ridges 33 extending axially between therecesses 32 are formed. Then, the unwoven fabric 13 and the cord 12 areprovided to be supported with the ridges 33.

Then, as shown in FIG. 3B, the inner mold 31 is housed in a cylindricalouter mold 34. At this time, a cavity C for molding the toothed beltbody is formed between the inner mold 31 and the outer mold 34.

Subsequently, as shown in FIG. 3C, a liquid urethan composition obtainedby blending a compound ingredient into a urethan prepolymer is injectedand charged into the closed cavity C. At this time, a toothed belt body11 of polyurethane resin is formed by the urethan composition flowingand cured. Further, the teeth 112 are formed in the recesses 32. Thecord 12 is adhered and embedded in the toothed belt body 11. The urethancomposition is impregnated into the unwoven fabric 13 and then cured,and the unwoven fabric 13 is adhered to and embedded in the toothed beltbody 11. In this way, the toothed belt body 11, the cord 12, and theunwoven fabric 13 are integrated to form a cylindrical belt slab S.

Finally, the belt slab S is demolded from the inner mold 31 and theouter mold 34, and cut into round slices, whereby the toothed belt Baccording to the embodiment is obtained.

In the embodiment described above, the toothed belt B is made of thetoothed belt body 11, the cord 12, and the unwoven fabric 13, but is notlimited thereto. A reinforcing fabric may be provided on the teeth faceon the inner periphery side of the toothed belt body and/or the backfaceon the outer periphery side of the toothed belt body.

In the embodiment, the toothed belt B includes a toothed belt body 11made of polyurethane resin, but is not particularly limited thereto. Thetoothed belt body itself may be formed of a crosslinking rubbercomposition.

In the embodiment, the toothed belt B is shown as a power transmissionbelt, but the power transmission belt is not particularly limitedthereto and may be a flat belt, a V-belt, a V-ribbed belt, or the like.

EXAMPLE

[Test Evaluation 1]

(Toothed Belt)

Toothed belts of Example 1 and Comparative Examples 1-1 and 1-2 wereprepared. Constituents of each belt will also be shown in Table 1.

Example 1

A STS toothed belt with the same configuration as in the embodiment wasprepared as Example 1. The toothed belt of Example 1 had a belt lengthof 1400 mm, a belt width of 14 mm, and a belt thickness (at maximum) of8.6 mm Teeth are S14M defined in ISO 13050: 2014 (E).

As the urethan composition for forming a toothed belt body, one obtainedby blending 13 parts by mass of 3,3′-dichloro-4,4′-diaminodiphenylmethane as a curing agent and 10 parts by mass of dioctylphthalate as a plasticizer to 100 parts by mass of urethan prepolymerwas used. A polyurethane resin which forms the toothed belt body had ahardness of 92°, measured based on JIS K7312.

As a cord, a single twist yarn obtained by twisting a filament bundle(the total number of filaments: 48000, a total fiber fineness: 3200 tex)in one direction with the number of twists of the cord per 10 cm lengthof 4/10 cm was used. The filament bundle was obtained by putting fourcarbon fibers each with the number of filaments of 12000 (TORAYCAT700SC-12000, manufactured by TORAY INDUSTRIES, INC., 12K, 800 tex, afilament diameter: 7 μm) together. The angle of the outermost filamentin the filament bundle of the carbon fibers forming the cord withrespect to the length direction of the cord was 10°. For the cord ofsingle twist yarn, a S-twist yarn and a Z-twist yarn were provided, andwere subjected to adhesion treatment of immersing them in an adhesiveand drying. The S-twist yarn and the Z-twist yarn which form a singletwist yarn for the cord were arranged alternately in the belt widthdirection to form a double helix pattern. The number of cords per 10 mmbelt width was four. The cord had a diameter of 2.0 mm.

As unwoven fabric, one made of nylon fibers and formed by needlepunching without pressurization was used. The unwoven fabric was notsubjected to adhesion treatment.

The toothed belt of Example 1 had a belt strength of 1302 N/mm per 1 mmbelt width. The belt tension T_(0.1) was 40.0 N/mm.

Comparative Example 1-1

A toothed belt with the same configuration as in Example 1 except that aplied yarn (the total number of filaments: 48000, the total fiberfineness: 3200 tex) made of carbon fibers was used as the cord wasprepared as Comparative Example 1-1. The plied yarn was produced asfollows: a filament bundle of carbon fibers with the number of filamentsof 12000, which was the same as used in Example 1, was twisted in onedirection with the number of twists per 10 cm length of four, therebyforming a first-twist yarn, and four of the first-twist yarn were thenput together and twisted in a direction opposite to the direction oftwisting the first-twist yarn, with the number of twists per 10 cmlength of four. The angle of the outermost filament in the filamentbundle of the carbon fibers forming the cord of the plied yarn withrespect to the length direction of the cord was 7°.

The toothed belt of Comparative Example 1-1 had a belt strength of 1267N/mm per 1 mm belt width. The belt tension T_(0.1) was 38.5 N/mm.

Comparative Example 1-2>

A toothed belt with the same configuration as in Example 1 except thatthe number of twists of the cord per 10 cm length was 6/10 cm wasprepared as Comparative Example 1-2. The angle of the outermost filamentin the filament bundle of the carbon fibers forming the cord withrespect to the length direction of the cord was 21°.

The toothed belt of Comparative Example 1-2 had a belt strength of 640N/mm per 1 mm belt width. The belt tension T_(0.1) was 41.0 N/mm.

TABLE 1 Comparative Comparative Example Example Example 1 1-1 1-2 ToothArrangement 14 14 14 Pitch (mm) Total Number 32000 32000 32000 ofFilaments Number of Twists 4 4 (First-Twist 6 (per 10 cm) Yarn)/4(Second- Twist Yarn) Angle θ of 10 7 21 Filament (°) Number of Cords 4 44 (per 10 mm) Belt Strength 1302 1267 640 (N/mm) Belt Tension 40.0 38.541.0 T_(0.1) (N/mm) Belt Durability 756 26 65 Life (hour)

(Belt Durability Test)

FIG. 4 shows a layout of pulleys in the belt running tester 40 used in abelt durability test. The belt running tester 40 includes a drive pulley41 with 22 teeth and a driven pulley 42 with 33 teeth, provided on theright side of the drive pulley 41. The driven pulley 42 is provided tobe movable to the left or right side, and is configured to be appliedwith an axial load and a load torque.

In a 60° C. atmosphere, each of the toothed belts B of Example 1 andComparative Examples 1-1 and 1-2 was wrapped around the drive pulley 41and the driven pulley 42, applied with a fixed axial load (SW) of 1960Nto apply tension of 1000N to the toothed belt B, and applied with a loadtorque of 120 N·m. In this state, the drive pulley 41 was rotated at thenumber of revolutions of 1800 rpm. Then, the time until the toothed beltB was broken was measured, and the time was used as a belt durabilitylife.

(Test Results)

Table 1 shows the test results. As can be seen, durability in Example 1was significantly higher than that in each of Comparative Examples 1-1and 1-2.

[Test Evaluation 2]

(Toothed Belt)

Toothed belts of Examples 2-1 and 2-2 and Comparative Examples 2-1 and2-2 were prepared. The configuration of each belt will also be shown inTable 2.

Example 2-1

A STS toothed belt with the same configuration as in the embodiment wasprepared as Example 2-1. The toothed belt of Example 2-1 had a beltlength of 800 mm, a belt width of 8 mm, and a belt thickness (atmaximum) of 4.8 mm. The teeth were S8M defined in ISO 13050: 2014 (E).

As a cord, a single twist yarn obtained by twisting a filament bundle ofcarbon fibers each with the number of filaments of 12000, which is thesame as the one used in Example 1, in one direction with the number oftwists per 10 cm length of 6/10 cm was used. The angle of the outermostfilament in the filament bundle of the carbon fibers forming the cordwith respect to the length direction of the cord was 9°. For the cord ofsingle twist yarn, a S-twist yarn and a Z-twist yarn were provided, andwere subjected to adhesion treatment of immersing them in an adhesiveand drying. The S-twist yarn and the Z-twist yarn which form a singletwist yarn for the cord were arranged alternately in the belt widthdirection to form a double helix pattern. The number of cords per 10 mmof the belt width was eight. The cord had a diameter of 0.9 mm.

The urethan composition for forming a toothed belt body and unwovenfabric were the same as those used in Example 1.

The toothed belt of Example 2-1 had a belt strength of 1150 N/mm per 1mm belt width. The belt tension T_(0.1) was 44.4 N/mm.

Example 2-2

A toothed belt with the same configuration as in Example 2-1 except thatthe number of twists of the cord per 10 cm length was 10/10 cm wasprepared as Example 2-2. The angle of the outermost filament in thefilament bundle of the carbon fibers forming the cord with respect tothe length direction of the cord was 19°.

The toothed belt of Example 2-2 had a belt strength of 738 N/mm per 1 mmbelt width. The belt tension T_(0.1) was 40.5 N/mm.

Comparative Example 2-1

A toothed belt with the same configuration as in Comparative Example 2-1except that the number of twists of the cord per 10 cm length was 4/10cm was prepared as Comparative Example 2-1. The angle of the outermostfilament in the filament bundle of the carbon fibers forming the cordwith respect to the length direction of the cord was 6°.

The toothed belt of Comparative Example 2-1 had a belt strength of 811N/mm per 1 mm belt width. The belt tension T_(0.1) was 32.7 N/mm.

Comparative Example 2-2

A toothed belt with the same configuration as in Example 2-1 except thatthe number of twists of the cord per 10 cm length was 12/10 cm wasprepared as Comparative Example 2-2. The angle of the outermost filamentin the filament bundle of the carbon fibers forming the cord withrespect to the length direction of the cord was 21°.

The toothed belt of Comparative Example 2-2 had a belt strength of 694N/mm per 1 mm belt width. The belt tension T_(0.1) was 42.8 N/mm.

TABLE 2 Comparative Comparative Example Example Example Example 2-1 2-22-1 2-2 Tooth Arrangement 8 8 8 8 Pitch (mm) Total Number 8000 8000 80008000 of Filaments Number of twists 6 10 4 12 (time/10 cm) Angle θ of 919 6 21 Filament (°) Number of Cords 8 8 8 8 (per 10 mm) Belt Strength1150 738 811 694 (N/mm) Belt Tension 44.4 40.5 32.7 42.8 T_(0.1) (N/mm)Belt Durability 270 491 41 81 Life (hour)

(Belt Durability Test)

Used was a belt running tester 40 with a layout of pulleys shown in FIG.4 , which was the same as used in Test Evaluation 1 except that thedrive pulley 41 and the driven pulley 42 were configured to be engagedwith teeth of the toothed belts B of Examples 2-1 and 2-2 andComparative Examples 2-1 and 2-2.

In a 60° C. atmosphere, each of the toothed belts B of Examples 2-1 and2-2 and Comparative Examples 2-1 and 2-2 was wrapped around the drivepulley 41 and the driven pulley 42, applied with a fixed axial load (SW)of 608N to apply tension of 306N to the toothed belt B, and applied witha load torque of 34.5 N·m. In this state, the drive pulley 41 wasrotated at the number of revolutions of 4218 rpm. Then, the time untilthe toothed belt B was broken was measured, and the time was used as abelt durability life.

(Test Results)

Table 2 shows the test results. As can be seen, the durability in eachof Examples 2-1 and 2-2 was significantly higher than that in each ofComparative Examples 2-1 and 2-2.

The embodiments have been described above as example techniques of thepresent disclosure, in which the attached drawings and the detaileddescription are provided. As such, elements illustrated in the attacheddrawings or the detailed description may include not only essentialelements for solving the problem, but also non-essential elements forsolving the problem in order to illustrate such techniques. Thus, themere fact that those non-essential elements are shown in the attacheddrawings or the detailed description should not be interpreted asrequiring that such elements be essential. Since the embodimentsdescribed above are intended to illustrate the techniques in the presentdisclosure, it is intended by the following claims to claim any and allmodifications, substitutions, additions, and omissions that fall withinthe proper scope of the claims appropriately interpreted in accordancewith the doctrine of equivalents and other applicable judicialdoctrines.

What is claimed is:
 1. A power transmission belt including a belt bodymade of an elastomer, and a cord made of carbon fibers and provided tobe embedded in the belt body and to form a helical pattern having apitch in a belt width direction, when the cord is viewed from a sideorthogonal to a length direction of the cord, an angle of an outermostfilament in a filament bundle of the carbon fibers forming the cord withrespect to the length direction of the cord being 8° or more to 20° orless.
 2. The power transmission belt of claim 1, wherein the belt bodyis made of a polyurethane resin.
 3. The power transmission belt of claim1, wherein the carbon fibers forming the cord are PAN-based carbonfibers.
 4. The power transmission belt of claim 1, wherein the carbonfibers have a filament diameter of 4 μm or more to 9 μm or less.
 5. Thepower transmission belt of claim 1, wherein a total number of filamentsof the carbon fibers forming the cord is 3000 or more to 60000 or less.6. The power transmission belt of claim 1, wherein the cord is a singletwist yarn obtained by twisting a filament bundle of the carbon fibersin one direction.
 7. The power transmission belt of claim 6, wherein inthe cord of the single twist yarn, a total number of filaments of thecarbon fibers forming the cord of the single twist yarn is 3000 or moreto less than 24000, and a number of twists of the cord per 10 cm lengthis 2.0/10 cm or more to 25.0/10 cm or less.
 8. The power transmissionbelt of claim 6, wherein in the cord of the single twist yarn, a totalnumber of filaments of the carbon fibers forming the cord of the singletwist yarn is 24000 or more to 60000 or less, and a number of twists ofthe cord per 10 cm length is 1.5/10 cm or more to 7.5/10 cm or less. 9.The power transmission belt of claim 1, wherein a number of cords per 10mm belt width is 3/10 mm or more to 16/10 mm or less.
 10. The powertransmission belt of claim 1, wherein the belt body is a toothed beltbody.
 11. The power transmission belt of claim 10, wherein a belttension T_(0.1) per 1 mm belt width at 0.1 of a belt extension rate is30 N/mm or more to 50 N/mm or less.